[libvirt] [PATCHv5 04/13] util: use SCM_RIGHTS in virFileOperation when needed
Eric Blake
eblake at redhat.com
Sat Mar 26 12:52:33 UTC 2011
Currently, the hook function in virFileOperation is extremely limited:
it must be async-signal-safe, and cannot modify any memory in the
parent process. It is much handier to return a valid fd and operate
on it in the parent than to deal with hook restrictions.
* src/util/util.h (VIR_FILE_OP_RETURN_FD): New flag.
* src/util/util.c (virFileOperationNoFork, virFileOperation):
Honor new flag.
---
v5: incorporate comments, such as closing fds sooner and switching
to SOCK_STREAM to avoid hangs
src/util/util.c | 138 ++++++++++++++++++++++++++++++++++++++++++++++++------
src/util/util.h | 4 +-
2 files changed, 125 insertions(+), 17 deletions(-)
diff --git a/src/util/util.c b/src/util/util.c
index 7c7da22..a0a331d 100644
--- a/src/util/util.c
+++ b/src/util/util.c
@@ -1428,14 +1428,15 @@ static int virFileOperationNoFork(const char *path, int openflags, mode_t mode,
if ((hook) && ((ret = hook(fd, hookdata)) != 0)) {
goto error;
}
+ if (flags & VIR_FILE_OP_RETURN_FD)
+ return fd;
if (VIR_CLOSE(fd) < 0) {
ret = -errno;
virReportSystemError(errno, _("failed to close new file '%s'"),
path);
- fd = -1;
goto error;
}
- fd = -1;
+
error:
VIR_FORCE_CLOSE(fd);
return ret;
@@ -1480,7 +1481,32 @@ error:
return ret;
}
-/* return -errno on failure, or 0 on success */
+/**
+ * virFileOperation:
+ * @path: file to open or create
+ * @openflags: flags to pass to open
+ * @mode: mode to use on creation or when forcing permissions
+ * @uid: uid that should own file on creation
+ * @gid: gid that should own file
+ * @hook: callback to run once file is open; see below for restrictions
+ * @hookdata: opaque data for @hook
+ * @flags: bit-wise or of VIR_FILE_OP_* flags
+ *
+ * Open @path, and execute an optional callback @hook on the open file
+ * description. @hook must return 0 on success, or -errno on failure.
+ * If @flags includes VIR_FILE_OP_AS_UID, then open the file while the
+ * effective user id is @uid (by using a child process); this allows
+ * one to bypass root-squashing NFS issues. If @flags includes
+ * VIR_FILE_OP_FORCE_PERMS, then ensure that @path has those
+ * permissions before the callback, even if the file already existed
+ * with different permissions. If @flags includes
+ * VIR_FILE_OP_RETURN_FD, then use SCM_RIGHTS to guarantee that any
+ * @hook is run in the parent, and the return value (if non-negative)
+ * is the file descriptor, left open. Otherwise, @hook might be run
+ * in a child process, so it must be async-signal-safe (ie. no
+ * malloc() or anything else that depends on modifying locks held in
+ * the parent), no file descriptor remains open, and 0 is returned on
+ * success. Return -errno on failure. */
int virFileOperation(const char *path, int openflags, mode_t mode,
uid_t uid, gid_t gid,
virFileOperationHook hook, void *hookdata,
@@ -1488,7 +1514,14 @@ int virFileOperation(const char *path, int openflags, mode_t mode,
struct stat st;
pid_t pid;
int waitret, status, ret = 0;
- int fd;
+ int fd = -1;
+ int pair[2] = { -1, -1 };
+ struct msghdr msg;
+ struct cmsghdr *cmsg;
+ char buf[CMSG_SPACE(sizeof(fd))];
+ char dummy = 0;
+ struct iovec iov;
+ int forkRet;
if ((!(flags & VIR_FILE_OP_AS_UID))
|| (getuid() != 0)
@@ -1502,7 +1535,29 @@ int virFileOperation(const char *path, int openflags, mode_t mode,
* following dance avoids problems caused by root-squashing
* NFS servers. */
- int forkRet = virFork(&pid);
+ if (flags & VIR_FILE_OP_RETURN_FD) {
+ if (socketpair(AF_UNIX, SOCK_STREAM, 0, pair) < 0) {
+ ret = -errno;
+ virReportSystemError(errno,
+ _("failed to create socket needed for '%s'"),
+ path);
+ return ret;
+ }
+
+ memset(&msg, 0, sizeof(msg));
+ iov.iov_base = &dummy;
+ iov.iov_len = 1;
+ msg.msg_iov = &iov;
+ msg.msg_iovlen = 1;
+ msg.msg_control = buf;
+ msg.msg_controllen = sizeof(buf);
+ cmsg = CMSG_FIRSTHDR(&msg);
+ cmsg->cmsg_level = SOL_SOCKET;
+ cmsg->cmsg_type = SCM_RIGHTS;
+ cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
+ }
+
+ forkRet = virFork(&pid);
if (pid < 0) {
ret = -errno;
@@ -1510,6 +1565,31 @@ int virFileOperation(const char *path, int openflags, mode_t mode,
}
if (pid) { /* parent */
+ if (flags & VIR_FILE_OP_RETURN_FD) {
+ VIR_FORCE_CLOSE(pair[1]);
+
+ do {
+ ret = recvmsg(pair[0], &msg, 0);
+ } while (ret < 0 && errno == EINTR);
+
+ if (ret < 0) {
+ ret = -errno;
+ VIR_FORCE_CLOSE(pair[0]);
+ while ((waitret = waitpid(pid, NULL, 0) == -1)
+ && (errno == EINTR));
+ goto parenterror;
+ }
+ VIR_FORCE_CLOSE(pair[0]);
+
+ /* See if fd was transferred. */
+ cmsg = CMSG_FIRSTHDR(&msg);
+ if (cmsg && cmsg->cmsg_len == CMSG_LEN(sizeof(fd)) &&
+ cmsg->cmsg_level == SOL_SOCKET &&
+ cmsg->cmsg_type == SCM_RIGHTS) {
+ memcpy(&fd, CMSG_DATA(cmsg), sizeof(fd));
+ }
+ }
+
/* wait for child to complete, and retrieve its exit code */
while ((waitret = waitpid(pid, &status, 0) == -1)
&& (errno == EINTR));
@@ -1520,12 +1600,20 @@ int virFileOperation(const char *path, int openflags, mode_t mode,
path);
goto parenterror;
}
- if (!WIFEXITED(status) || (ret = -WEXITSTATUS(status)) == -EACCES) {
+ if (!WIFEXITED(status) || (ret = -WEXITSTATUS(status)) == -EACCES ||
+ ((flags & VIR_FILE_OP_RETURN_FD) && fd == -1)) {
/* fall back to the simpler method, which works better in
* some cases */
return virFileOperationNoFork(path, openflags, mode, uid, gid,
hook, hookdata, flags);
}
+ if (!ret && (flags & VIR_FILE_OP_RETURN_FD)) {
+ if ((hook) && ((ret = hook(fd, hookdata)) != 0)) {
+ VIR_FORCE_CLOSE(fd);
+ goto parenterror;
+ }
+ ret = fd;
+ }
parenterror:
return ret;
}
@@ -1535,6 +1623,7 @@ parenterror:
if (forkRet < 0) {
/* error encountered and logged in virFork() after the fork. */
+ ret = -errno;
goto childerror;
}
@@ -1584,15 +1673,32 @@ parenterror:
path, mode);
goto childerror;
}
- if ((hook) && ((ret = hook(fd, hookdata)) != 0)) {
- goto childerror;
- }
- if (VIR_CLOSE(fd) < 0) {
- ret = -errno;
- virReportSystemError(errno, _("child failed to close new file '%s'"),
- path);
- goto childerror;
+ if (flags & VIR_FILE_OP_RETURN_FD) {
+ VIR_FORCE_CLOSE(pair[0]);
+ memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
+
+ do {
+ ret = sendmsg(pair[1], &msg, 0);
+ } while (ret < 0 && errno == EINTR);
+
+ if (ret < 0) {
+ ret = -errno;
+ goto childerror;
+ }
+ ret = 0;
+ } else {
+ if ((hook) && ((ret = hook(fd, hookdata)) != 0))
+ goto childerror;
+ if (VIR_CLOSE(fd) < 0) {
+ ret = -errno;
+ virReportSystemError(errno,
+ _("child failed to close new file '%s'"),
+ path);
+ goto childerror;
+ }
}
+
+ ret = 0;
childerror:
/* ret tracks -errno on failure, but exit value must be positive.
* If the child exits with EACCES, then the parent tries again. */
@@ -1719,7 +1825,7 @@ int virFileOperation(const char *path ATTRIBUTE_UNUSED,
virUtilError(VIR_ERR_INTERNAL_ERROR,
"%s", _("virFileOperation is not implemented for WIN32"));
- return -1;
+ return -ENOSYS;
}
int virDirCreate(const char *path ATTRIBUTE_UNUSED,
@@ -1731,7 +1837,7 @@ int virDirCreate(const char *path ATTRIBUTE_UNUSED,
virUtilError(VIR_ERR_INTERNAL_ERROR,
"%s", _("virDirCreate is not implemented for WIN32"));
- return -1;
+ return -ENOSYS;
}
#endif /* WIN32 */
diff --git a/src/util/util.h b/src/util/util.h
index 0f11f8f..b1ca871 100644
--- a/src/util/util.h
+++ b/src/util/util.h
@@ -130,12 +130,14 @@ enum {
VIR_FILE_OP_NONE = 0,
VIR_FILE_OP_AS_UID = (1 << 0),
VIR_FILE_OP_FORCE_PERMS = (1 << 1),
+ VIR_FILE_OP_RETURN_FD = (1 << 2),
};
typedef int (*virFileOperationHook)(int fd, void *data);
int virFileOperation(const char *path, int openflags, mode_t mode,
uid_t uid, gid_t gid,
virFileOperationHook hook, void *hookdata,
- unsigned int flags) ATTRIBUTE_RETURN_CHECK;
+ unsigned int flags)
+ ATTRIBUTE_NONNULL(1) ATTRIBUTE_RETURN_CHECK;
enum {
VIR_DIR_CREATE_NONE = 0,
--
1.7.4
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